The present invention relates to material handling apparatus, and more particularly to a portable utility crane or derrick mountable on a pickup truck or on a trailer.
In many industries a need exists for a temporary or portable hoist which can be transported to a work site, quickly and easily erected and which may be easily operated. In the construction industry, for example, portable cranes are used to lift materials, and to install air conditioning systems, roof antennas, signs, trusses, and the like. In the majority of these operations, large cranes are not needed. The load carrying capacity of a large self propelled derrick or crane vehicles greatly exceeds the loads which would be encountered in the general contracting industry.
In order to fulfill these needs, various portable crane or derrick assemblies have been proposed. Many of the prior systems have suffered from undue complexity and lack of versatility. U.S. Pat. No. 3,797,672 to Vermette entitled APPARATUS ATTACHABLE TO A TRUCK BODY OR THE LIKE FOR USE FOR HOISTING OR LIFTING, OR AS AN ELEVATED SUPPORT, issued May 19, 1974, discloses a device having a frame attachable to stake holes of a pickup truck. The device supports a single, vertically extending boom. Attached to the top of the boom is crossmember to which a cable hoist is secured. The boom is collapsible to permit transportation of the apparatus.
Many of the problems, heretofore, experienced are addressed in the commonly owned prior patents of the present inventors, including U.S. Pat. No. 4,068,762 entitled PICKUP TRUCK DERRICK, issued on Jan. 17, 1978; U.S. Pat. No. 4,615,450 entitled PORTABLE AND COLLAPSIBLE DERRICK STRUCTURE, which issued on Oct. 7, 1986, and U.S. Pat. No. 4,651,884 entitled PORTABLE AND COLLAPSIBLE DERRICK STRUCTURE, which issued on Mar. 24, 1987. The '762 patent discloses an improved, portable hoist or derrick assembly which includes a rectangular base frame securable to the side rails of a conventional pickup truck. A collapsible A-frame is pivotally mounted on the base frame. Provision is made for supporting the A-frame and for erecting the A-frame to a vertical position. A foldable, two-piece boom assembly is pivotally and swingably carried on an A-frame support plate. Provision is made for erecting the boom from a folded stored position, for elevating the boom during hoisting operations and for swinging the boom about a vertical axis. The '450 and '884 patents disclose various improvements in the derrick structure of the '762 patent. As disclosed therein, provision is made for elevating the A-frame and locking the frame in an operating position. Different forms of frame erection subassembies including an elongated track, roller and carriage arrangement are disclosed. In another form, the erection subassembly includes lead screw actuators, combined with support braces.